SQLite

  if( pIndex ){
    while( z[0] ){
      for(i=1; z[i] && z[i]!=' '; i++){}
      if( i==9 && memcmp(z, "unordered", 9)==0 ){
        pIndex->bUnordered = 1;
      }else if( i>2 && memcmp(z, "r=", 2)==0
                && sqlite3GetInt32(z+2, &v32) ){
        if( v32>255 ) v32 = 255;

        if( v32<0 ) v32 = 0;




        pIndex->iScanRatio = (u8)v32;
      }
      z += i;
      if( z[0]==' ' ) z++;
    }
  }
}

        KeyInfo *pKeyInfo = 0;               /* Keyinfo for scanned index */
        Index *pBest = 0;                    /* Best index found so far */
        int iRoot = pTab->tnum;              /* Root page of scanned b-tree */

        sqlite3CodeVerifySchema(pParse, iDb);
        sqlite3TableLock(pParse, iDb, pTab->tnum, 0, pTab->zName);

        /* Search for the index that has the least amount of columns. If
        ** there is such an index, and it has less columns than the table
        ** does, then we can assume that it consumes less space on disk and
        ** will therefore be cheaper to scan to determine the query result.
        ** In this case set iRoot to the root page number of the index b-tree
        ** and pKeyInfo to the KeyInfo structure required to navigate the
        ** index.
        **
        ** (2011-04-15) Do not do a full scan of an unordered index.
        **
        ** In practice the KeyInfo structure will not be used. It is only 
        ** passed to keep OP_OpenRead happy.
        */
        for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
          if( pIdx->bUnordered==0 && (!pBest || pIdx->nColumn<pBest->nColumn) ){



            pBest = pIdx;
          }
        }
        if( pBest && pBest->nColumn<pTab->nCol ){
          iRoot = pBest->tnum;
          pKeyInfo = sqlite3IndexKeyinfo(pParse, pBest);
        }

        /* Open a read-only cursor, execute the OP_Count, close the cursor. */
        sqlite3VdbeAddOp3(v, OP_OpenRead, iCsr, iRoot, iDb);
        if( pKeyInfo ){

    if( pProbe->tnum<=0 ){
      /* Integer primary key index */
      pNew->wsFlags = WHERE_IPK;

      /* Full table scan */
      pNew->iSortIdx = b ? iSortIdx : 0;
      /* TUNING: Cost of full table scan is 3*(N + log2(N)).
      **  +  The extra 3 factor is to encourage the use of indexed lookups
      **     over full scans.  A smaller constant 2 is used for covering
      **     index scans so that a covering index scan will be favored over
      **     a table scan. */
      pNew->rRun = whereCostAdd(rSize,rLogSize) + 16;
      whereLoopOutputAdjust(pWC, pNew, pSrc->iCursor);
      rc = whereLoopInsert(pBuilder, pNew);
      pNew->nOut = rSize;
      if( rc ) break;
    }else{
      Bitmask m = pSrc->colUsed & ~columnsInIndex(pProbe);
      pNew->wsFlags = (m==0) ? (WHERE_IDX_ONLY|WHERE_INDEXED) : WHERE_INDEXED;

      /* Full scan via index */
      if( b
       || ( m==0
         && pProbe->bUnordered==0

         && (pWInfo->wctrlFlags & WHERE_ONEPASS_DESIRED)==0
         && sqlite3GlobalConfig.bUseCis
         && OptimizationEnabled(pWInfo->pParse->db, SQLITE_CoverIdxScan)
          )
      ){
        pNew->iSortIdx = b ? iSortIdx : 0;
        if( m==0 ){
          /* TUNING: Cost of a covering index scan is 2*(N + log2(N)).

          **  +  The extra 2 factor is to encourage the use of indexed lookups
          **     over index scans.  A table scan uses a factor of 3 so that
          **     index scans are favored over table scans.
          **  +  If this covering index might also help satisfy the ORDER BY
          **     clause, then the cost is fudged down slightly so that this
          **     index is favored above other indices that have no hope of
          **     helping with the ORDER BY. */
          pNew->rRun = 10 + whereCostAdd(rSize,rLogSize) - b;
        }else{
          assert( b!=0 ); 
          /* TUNING: Cost of scanning a non-covering index is (N+1)*log2(N)
          ** which we will simplify to just N*log2(N) */
          pNew->rRun = rSize + rLogSize;
        }
        whereLoopOutputAdjust(pWC, pNew, pSrc->iCursor);

proc eqp {sql {db db}} {
  uplevel execsql [list "EXPLAIN QUERY PLAN $sql"] $db
}

do_test analyze6-1.0 {
  db eval {
    CREATE TABLE cat(x INT);
    CREATE UNIQUE INDEX catx ON cat(x);
    /* Give cat 16 unique integers */
    INSERT INTO cat VALUES(1);
    INSERT INTO cat VALUES(2);
    INSERT INTO cat SELECT x+2 FROM cat;
    INSERT INTO cat SELECT x+4 FROM cat;
    INSERT INTO cat SELECT x+8 FROM cat;

    CREATE TABLE ev(y INT);
    CREATE INDEX evy ON ev(y);
    /* ev will hold 32 copies of 16 integers found in cat */
    INSERT INTO ev SELECT x FROM cat;
    INSERT INTO ev SELECT x FROM cat;
    INSERT INTO ev SELECT y FROM ev;

# ...
# eqp-7.*:        "SELECT count(*) FROM tbl" statements (VDBE code OP_Count).
#

proc det {args} { uplevel do_eqp_test $args }

do_execsql_test 1.1 {
  CREATE TABLE t1(a, b);
  CREATE INDEX i1 ON t1(a);
  CREATE INDEX i2 ON t1(b);
  CREATE TABLE t2(a, b);
  CREATE TABLE t3(a, b);
}

do_eqp_test 1.2 {
  SELECT * FROM t2, t1 WHERE t1.a=1 OR t1.b=2;
} {
  0 0 1 {SEARCH TABLE t1 USING INDEX i1 (a=?)} 
  0 0 1 {SEARCH TABLE t1 USING INDEX i2 (b=?)} 

}

#-------------------------------------------------------------------------
# Test cases eqp-2.* - tests for single select statements.
#
drop_all_tables
do_execsql_test 2.1 {
  CREATE TABLE t1(x, y);

  CREATE TABLE t2(x, y);
  CREATE INDEX t2i1 ON t2(x);
}

det 2.2.1 "SELECT DISTINCT min(x), max(x) FROM t1 GROUP BY x ORDER BY 1" {
  0 0 0 {SCAN TABLE t1}
  0 0 0 {USE TEMP B-TREE FOR GROUP BY}
  0 0 0 {USE TEMP B-TREE FOR DISTINCT}

#
drop_all_tables

# EVIDENCE-OF: R-47779-47605 sqlite> EXPLAIN QUERY PLAN SELECT a, b
# FROM t1 WHERE a=1;
# 0|0|0|SCAN TABLE t1
#
do_execsql_test 5.1.0 { CREATE TABLE t1(a, b) }
det 5.1.1 "SELECT a, b FROM t1 WHERE a=1" {
  0 0 0 {SCAN TABLE t1}
}

# EVIDENCE-OF: R-55852-17599 sqlite> CREATE INDEX i1 ON t1(a);
# sqlite> EXPLAIN QUERY PLAN SELECT a, b FROM t1 WHERE a=1;
# 0|0|0|SEARCH TABLE t1 USING INDEX i1

}

# EVIDENCE-OF: R-09991-48941 sqlite> EXPLAIN QUERY PLAN
# SELECT t1.*, t2.* FROM t1, t2 WHERE t1.a=1 AND t1.b>2;
# 0|0|0|SEARCH TABLE t1 USING COVERING INDEX i2 (a=? AND b>?)
# 0|1|1|SCAN TABLE t2
#
do_execsql_test 5.4.0 {CREATE TABLE t2(c, d)}
det 5.4.1 "SELECT t1.*, t2.* FROM t1, t2 WHERE t1.a=1 AND t1.b>2" {
  0 0 0 {SEARCH TABLE t1 USING COVERING INDEX i2 (a=? AND b>?)}
  0 1 1 {SCAN TABLE t2}
}

# EVIDENCE-OF: R-33626-61085 sqlite> EXPLAIN QUERY PLAN
# SELECT t1.*, t2.* FROM t2, t1 WHERE t1.a=1 AND t1.b>2;
# 0|0|1|SEARCH TABLE t1 USING COVERING INDEX i2 (a=? AND b>?)
# 0|1|0|SCAN TABLE t2
#
det 5.5 "SELECT t1.*, t2.* FROM t2, t1 WHERE t1.a=1 AND t1.b>2" {
  0 0 1 {SEARCH TABLE t1 USING COVERING INDEX i2 (a=? AND b>?)}
  0 1 0 {SCAN TABLE t2}
}

# EVIDENCE-OF: R-04002-25654 sqlite> CREATE INDEX i3 ON t1(b);
# sqlite> EXPLAIN QUERY PLAN SELECT * FROM t1 WHERE a=1 OR b=2;
# 0|0|0|SEARCH TABLE t1 USING COVERING INDEX i2 (a=?)
# 0|0|0|SEARCH TABLE t1 USING INDEX i3 (b=?)
#
do_execsql_test 5.5.0 {CREATE INDEX i3 ON t1(b)}
det 5.6.1 "SELECT * FROM t1 WHERE a=1 OR b=2" {
  0 0 0 {SEARCH TABLE t1 USING COVERING INDEX i2 (a=?)}
  0 0 0 {SEARCH TABLE t1 USING INDEX i3 (b=?)}
}

# EVIDENCE-OF: R-24577-38891 sqlite> EXPLAIN QUERY PLAN
# SELECT c, d FROM t2 ORDER BY c;
# 0|0|0|SCAN TABLE t2

}

# EVIDENCE-OF: R-46219-33846 sqlite> EXPLAIN QUERY PLAN
# SELECT * FROM (SELECT * FROM t2 WHERE c=1), t1;
# 0|0|0|SEARCH TABLE t2 USING INDEX i4 (c=?)
# 0|1|1|SCAN TABLE t1
#
det 5.11 "SELECT * FROM (SELECT * FROM t2 WHERE c=1), t1" {
  0 0 0 {SEARCH TABLE t2 USING INDEX i4 (c=?)}
  0 1 1 {SCAN TABLE t1 USING COVERING INDEX i2}
}

# EVIDENCE-OF: R-37879-39987 sqlite> EXPLAIN QUERY PLAN
# SELECT a FROM t1 UNION SELECT c FROM t2;
# 1|0|0|SCAN TABLE t1

#-------------------------------------------------------------------------
# The following tests - eqp-7.* - test that queries that use the OP_Count
# optimization return something sensible with EQP.
#
drop_all_tables

do_execsql_test 7.0 {
  CREATE TABLE t1(a, b);
  CREATE TABLE t2(a, b);
  CREATE INDEX i1 ON t2(a);
}

det 7.1 "SELECT count(*) FROM t1" {
  0 0 0 {SCAN TABLE t1}
}